Credit card fraud is now becoming a substantial problem due to the ease with which magnetic stripe memories can be modified and copied. This problem also exists in the field of security cards and prepaid card systems.
Methods have been proposed to overcome the above problems employing holographic patterns and kinegrams.
For example a known kinegram card contains a computer generated holographic pattern extending along one or more tracks across the card. The pattern resembles a conventional hologram but is much brighter and can be made to display a greater degree of movement when viewed at different angles. When the card is used, for example when making a telephone call, it is inserted in a reader slot and the available balance is displayed. After connection, the equipment automatically emits metering pulses. The pulses sequentially decrement the card by destroying each bit by thermal energy. The hologram is read by directing at the pattern light, which is reflected. The angle of reflection is in a direction determined by the hologram. A detector is positioned to be activated by the reflected light.
Swiss Patent 622896 (Application No 2995/78) describes the use of a hologram, in which the reflected light includes a first reflected beam detected by a first sensor, while a second sensor detects scattered light reflected in a second direction. More particularly, the light reflected in the second direction includes a narrow beam and a diverging beam. The narrow beam is blocked so that only the diverging beam is delivered to the second sensor.
Australian Patent Application 19576/83 describes the use of kinegrams for visual verification of the authenticity of the article carrying the kinegram. The kinegram provides diffractive images which move in a predetermined manner with a change in relative orientation. There is no consideration of nor is this particular arrangement adapted to be machine readable.
Similarly Australian Patent Application 44674/85 describes the use of diffractive patterns and the use regarding visual security elements. Similarly Australian Applications 30841/89 and 53729/90 describe techniques for producing visual security images.
European Patent Application 81110234.2 (Publication No 0 060 937) describes the use of optical marks on numerical rollers of a counter mechanism. The optical marks can be a reflective hologram or a refractive grid. A reading beam is directed at each mark and a single beam reflected. Each mark directs the reflected beam at a different angle, with a plurality of detectors being arranged to be illuminated by the appropriate beam.
Swiss Patent Application No 16084/76 (Patent 604279) describes the use of discrete optical marks (which may consist of a diffractive grating or a hologram) which are erased to record information. There is little discussion of reading techniques and the properties of the optical marks.
European Patent Publication 0 015 307 (European Application 79104004.1) describes the use of a stored value card. The card has a series of optical marks arranged in discrete units. The marks are sequentially erased in order to decrease the value of the card.
Swiss Patent 638632 (Application No 929/79) also describes the use of optical marks on a card. The marks are arranged in a predetermined order and are used for identification purposes.
Swiss Patent Application 6836/81 shows the use of optical marks for the purposes of determining the authenticity of a document. The reading beam changes in wavelength which alters the direction of the refracted beam. A detector is then used to determine this change in direction as a means of determining the authenticity of the document.
European Patent Publication 0 051 271 (European Application No 81109503.3) describes the use of optical markings to produce two refracted narrow light beams. Measurement of the intensity of the light beams is used to verify the authenticity of the document.
European Publication No 0 366 585 (Application No 89108121.8) discloses the use of diffraction gratings arranged in a bar code. However the bars are applied to the carrier in a predetermined order in order to record information.
The above discussed optical diffraction techniques still lend themselves to unauthorised use particularly unauthorised reproduction of the holograms, and/or are not suitable for normal commercial use.
A stored value system is one in which the user purchases a memory device which represents usage of some service or facility up to a certain value. A good example can be found in many telephone systems, where users can purchase a stored value card which allows usage of the telephone system up to a specified value.
A stored value system depends on being able to sell to the user a memory device which can be altered to reflect usage of the system. This memory usually comes in the form of a card, a good example being a telephone card. The requirements on this stored value card are that it should be inexpensive; it must contain a write-once stored value memory so that once the value of the card has been decremented, the decrement is permanent; it should resist copying or fraudulent production; and preferably it should be capable of retaining a large number of the units of value for the system, so that the user does not have to replace the card too frequently.
These requirements together place restrictions on the technologies which can be applied to stored value memories. In general the stored value memories currently in use do not meet all of these requirements. For example, optical memories are used in stored value telephone cards in some countries, but these are generally limited to a relatively small number (several hundred or so) of stored value units, making them unsuitable for a number of other potential applications.